The present invention relates to an electrical device for rail mounting. Such electrical devices are mounted in use in a side-by-side relationship on a carrier rail, the so-called DIN rail (also known as top hat rail according to the European standard EN 50022, in the USA called TS35 rail). The present invention can be used with devices such as circuit breakers, fuse units, safety switching and control devices, and rail mounted power supplies, to name only a few.
Conventional rail mounted electrical devices comprise an electrically insulating housing that is shaped at one side to engage a carrier rail. At this side, the housing has a dovetail shaped transversely extending recess within which the rail is gripped in use. One side of this recess is defined by a latch member movable relatively to the housing to permit a snap-on engagement and disengagement of the housing and the rail, and the latch member is resiliently biased relative to the housing in a direction to reduce the width of the recess and thus to grip the rail in use.
Where one of the known devices is utilized alone then it is necessary to hold the latch member in a retracted position against the action of its resilient bias, while manipulating the device to disengage it from the rail. Such a mode of operation is inconvenient, but it will be realized that where a device comprises two or more units physically secured together, for handling as a unitary structure, as would be the case with two or more ganged isolators, then it is extremely difficult to hold two or more latches in their retracted position while manipulating the unitary structure relative to the rail.
In an attempt to overcome this problem it has previously been proposed to incorporate into each device a catch element movable manually, transversely relative to the latch member and cooperating with the housing to permit locking of the latch member in a retracted position. The provision of such a catch member simplifies operation by permitting latch members to be locked in their retracted positions but of course increases the complexity, and therefore cost of each unit.
Consequently, GB 2216177 A1 proposes an electrical device for rail mounting comprising a housing having a rail receiving recess therein, one edge of said recess being defined by an end region of a latch member movable relative to the housing in a direction transverse to the recess, resilient means biasing the latch member to move relative to the housing in a direction to reduce the width of said recess, and, interengagable surfaces on the housing and the latch member respectively which cooperate, when the latch member is retracted to a predetermined position against the action of said resilient means, to retain the latch member in said retracted position, said surfaces being such that the latch member can be released for movement under the action of said resilient means by a movement of the latch member relative to the housing in a direction transverse to the direction of movement of the latch member under the action of said resilient means.
This known solution, however, has the disadvantage that a compression spring is needed for biasing the latch member, which is space consuming and complicates the assembly process.
Consequently, there is still a need for an electrical device that can be mounted on a DIN rail efficiently, securely, and precisely, while the electrical device can be fabricated in a particularly cost-efficient way.